1. Technical Field
This invention relates generally to vehicle air-conditioning systems wherein air flows in first and second passages can be controlled to different values, and particularly to a reduced-cost system in which a cooling degree detector is provided only in the first passage, and in which the degree of cooling taking place in the second passage is estimated.
2. Related Art
As disclosed in Japanese Unexamined Patent Publication No. Hei. 9-39544, air-conditioning systems wherein the inside of an air-conditioner case is partitioned into two passages to form separate driver seat side and passenger seat side passages are well known. In such a system, an evaporator and a heater core extend across both passages. A driver seat side air-mixing door is provided in the driver seat side passage, and a passenger seat side air-mixing door is provided in the passenger seat side passage so that conditioned air temperatures can be separately matched to the preferences of a driver and a passenger.
Also in such a system, a single air-conditioning fan is disposed in a non-partitioned upstream part of the air-conditioner case. Consequently, the air flows passing through the two passages are the same.
In the above-described system, the conditioned air blown to the driver seat side and the passenger seat side is independently temperature-controlled. However, because the conditioned air is blown at the same rate to each side, it is not possible to independently control the air flow rate.
In systems utilizing the above type of independent temperature control scheme, a cooling degree detector for detecting the degree to which air is being cooled by an evaporator is provided on the downstream side of the evaporator. This detector produces a detection signal that is used as air-conditioning control information. However, when as mentioned above air flows in the passages are controlled to different values, at times the flow through a part of the evaporator is large while the flow through the remainder of the evaporator is small, as conditioned air in each of the two separate passages passes through the evaporator.
Consequently, to obtain accurate air-conditioning control information for each of the two passages, a detector must be provided on the downstream side of the evaporator in each of the two passages because the air flow in each passage, as well as the degree to which the air is cooled in each passage, is different.
However, providing a separate detector for each passage increases the number of system parts, labor required to assemble the system, and system cost. On the other hand, in the above-described air-conditioning system, it is difficult to prevent frosting of the evaporator while preventing a windshield from being fogged.